CHARA Community Workshop

Data Format, Modeling, Data Format, Modeling, and Imaging and Imaging

Data Format, Modeling, Data Format, Modeling, and Imaging and Imaging

Gail Schaefer

The CHARA Array ofGeorgia State University

Mount Wilson, CA

With contributions from:Fabien Baron and Laurent Bourgès

CHARA Community Workshop

Data ReductionData ReductionData ReductionData Reduction

● CHARA staff and consortium members will support data reduction to OIFITS format

● Many users may find it informative to run reduction software and calibration themselves

● Data analysis, model fitting, image reconstruction performed by users

CHARA Community Workshop

OIFITS FormatOIFITS FormatOIFITS FormatOIFITS Format

● OIFITS: Data exchange standard for Optical Interferometry

● Target and instrument information tables:

– OI_TARGET

– OI_ARRAY

– OI_WAVELENGTH

● Data tables:

– OI_VIS2

– OI_T3

CHARA Community Workshop

OI_VIS2 Table (OIFITS)OI_VIS2 Table (OIFITS)OI_VIS2 Table (OIFITS)OI_VIS2 Table (OIFITS)

TARGET_ID Target number

TIME UTC time of observation (s)

MJD Modified Julian Date

INT_TIME Integration time (s)

VIS2DATA Squared Visibility

VIS2ERR Error in Squared Visibility

UCOORD U coordinate of data (m)

VCOORD V coordinate of data (m)

STA_INDEX Station numbers

FLAG Flag

CHARA Community Workshop

OI_T3 Table (OIFITS)OI_T3 Table (OIFITS)OI_T3 Table (OIFITS)OI_T3 Table (OIFITS)

TARGET_ID Target number

TIME UTC time of observation (s)

MJD Modified Julian Date

INT_TIME Integration time (s)

T3AMP Triple Product Amplitude

T3AMPERR Error in Triple Product Amplitude

T3PHI Triple Product Phase in degrees

T3PHIERR Error in Triple Product Phase in degrees

U1COORD U coordinate of baseline AB in triangle (m)

V1COORD V coordinate of baseline AB in triangle (m)

U2COORD U coordinate of baseline BC in triangle (m)

V2COORD V coordinate of baseline BC in triangle (m)

STA_INDEX Station numbers

FLAG Flag

CHARA Community Workshop

Software for Reading/WritingSoftware for Reading/WritingOIFITS FilesOIFITS Files

Software for Reading/WritingSoftware for Reading/WritingOIFITS FilesOIFITS Files

● OIFITSlib – C Library– https://github.com/jsy1001/oifitslib

● IDL OIFITS Library – by John Monnier– http://dept.astro.lsa.umich.edu/~monnier/oi_data/

● OIFITS Explorer – by JMMC– http://www.jmmc.fr/oifitsexplorer_page.htm

● OITOOLS.jl – in development by Fabien Baron– Data visualization and modeling (Julia)

CHARA Community Workshop

OIFITS Explorer OIFITS Explorer OIFITS Explorer OIFITS Explorer

● Visualization

● Load OIFits files

● Plots:

– uv coverage

– V2, T3, ...

– HA, PA, SNR

● Future:

– Editor: flag and export merged OIFITS files

– Better data selection graphically

CHARA Community Workshop

Data AnalysisData AnalysisData AnalysisData Analysis

● Interferometers measure the Fourier Transform of the brightness distribution

● Sparse sampling

● Geometric model fitting

● Physical models

● Image reconstruction

CHARA Community Workshop

Model Fitting: LITproModel Fitting: LITproModel Fitting: LITproModel Fitting: LITpro

http://www.jmmc.fr/litpro_page.htm

● Fit geometric and limb-darkened models

● Plots to visualize data, models, and results of fits

● Tools to find global minimum

CHARA Community Workshop

Model Fitting: Model Fitting: Companion Search - CANDIDCompanion Search - CANDID

Model Fitting: Model Fitting: Companion Search - CANDIDCompanion Search - CANDID

Gallenne et al. (2015)

● Companion Analysis and Non-Detection in Interferometric Data

● Grid search for binary companions

● Estimate detection limits● https://github.com/amerand/CANDID

CHARA Community Workshop

Model Fitting: SIMTOIModel Fitting: SIMTOIModel Fitting: SIMTOIModel Fitting: SIMTOI

● SIMTOI: SImulation and Modeling Tool for Optical Interferometry

● Written by Brian Kloppenborg

● GPU accelerated

● Photometry + interferometry

● Physical models

● Global optimization

● Keplerian orbits

https://github.com/bkloppenborg/simtoi

CHARA Community Workshop

Image ReconstructionImage ReconstructionImage ReconstructionImage Reconstruction

● Sparse sampling of Fourier frequencies in plane of sky

● Inverse Fourier transform to obtain image

● Compromise between:

– Fitting available data

– Keeping the image as regular (simple) as possible

CHARA Community Workshop

Regularizationweight

Regularizer:Helps interpolate missing

Fourier data (smoothness, compactness, total variation,

maximum entropy)

Likelihood term:Comparison ofmodel to data

Regularized maximum likelihood

Most probable image

Image ReconstructionImage ReconstructionImage ReconstructionImage Reconstruction

CHARA Community Workshop

Image Reconstruction SoftwareImage Reconstruction SoftwareImage Reconstruction SoftwareImage Reconstruction Software

Software Optimization Regularizer Multi-Spectral

Simultaneous Model Fitting

BSMEM Trust region gradient

Maximum Entropy Method

No No

MACIM Simulated annealing

Maximum Entropy Method, Darkness

No Yes

MiRA Variable Metric Limited Memory with bound constraints

Many No Yes

SQUEEZE Parallel Tempering Many Yes Yes

PAINTER Alternating Direction Method of Minimizers

Many Yes No

CHARA Community Workshop

Imaging TutorialImaging TutorialImaging TutorialImaging Tutorial

JMMC is developing a commoninterface for “classic” image

reconstruction softwarehttp://www.jmmc.fr/oimaging.htm

CHARA Community Workshop

Different Reconstruction Different Reconstruction Methods and RegularizersMethods and RegularizersDifferent Reconstruction Different Reconstruction

Methods and RegularizersMethods and RegularizersOriginal Image

(LkHα 101)BSMEM MiRA + MEM

regularizer

MiRA + compactnessquadratic

MiRA + edge-preserving

SQUEEZE with l0 norm

wavelet coefficients

Thiebaut& Young(2017)

CHARA Community Workshop

AZ Cyg

2012 IAU Interferometry Beauty Contest

Baron et al. 2012

Truth/Model

High Fidelity Imaging of High Fidelity Imaging of Complex Targets is DifficultComplex Targets is Difficult

High Fidelity Imaging of High Fidelity Imaging of Complex Targets is DifficultComplex Targets is Difficult

CHARA Community Workshop

Baron et al., in prep

Isotropicwavelets

Arclets

Gradient

Sparsity basis

Ongoing Research on Ongoing Research on Better RegularizationBetter RegularizationOngoing Research on Ongoing Research on Better RegularizationBetter Regularization

CHARA Community Workshop

Regularization WeightRegularization WeightRegularization WeightRegularization Weight

Images by E. Thiebaut (MiRA)courtesy of F. Baron

CHARA Community Workshop

Images by S. RenardSee Renard et al., 2011

Avoid under and over Avoid under and over regularizationregularization

Avoid under and over Avoid under and over regularizationregularization

CHARA Community Workshop

Total variation Uniform disc regularizer

This method will help identify the best regularization

Artifact Detection Artifact Detection Fabien BaronFabien BaronArtifact Detection Artifact Detection Fabien BaronFabien Baron

● Use two control sets:

– model image of object with complexity (e.g., spotted star)

– much simpler model image with no features (e.g. limb-darkened disk)

● Simulate observations – copy Fourier coverage and signal to noise from original data

● Reconstruct images for two control data sets and check fidelity of reconstuctions

● Were spurious features introduced in simple model?

● Were feature correctly recovered in the complex model?

CHARA Community Workshop

Links for modeling and Links for modeling and imaging software available imaging software available

on the CHARA website:on the CHARA website:

http://www.chara.gsu.edu/analysis-software/http://www.chara.gsu.edu/analysis-software/

Links for modeling and Links for modeling and imaging software available imaging software available

on the CHARA website:on the CHARA website:

http://www.chara.gsu.edu/analysis-software/http://www.chara.gsu.edu/analysis-software/